Vehicle braking systems with automatic slack adjusters

ABSTRACT

A vehicle braking system includes a piston rod extendable from an air brake chamber, a rotatable cam shaft, and a slack adjuster coupled to the piston rod and the cam shaft. The slack adjuster is configured to rotate the cam shaft as the piston rod extends. The slack adjuster has a control gear coupled to the cam shaft such that the control gear rotates as the cam shaft is rotated. A pinion gear meshes with the control gear such that the pinion gear rotates as the control gear rotates, and a take-off gear meshes with the pinion gear such that the take-off gear rotates as the control gear rotates. A magnet coupled to the take-off gear is configured to rotate as the take-off gear rotates. A sensor is configured to sense rotation of the magnet, and an indicator is configured to indicate brake stroke of the piston rod.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation application of U.S. patentapplication Ser. No. 15/668,328, filed Aug. 3, 2017, which claims thebenefit of U.S. Provisional Patent Application No. 62/370,772, filedAug. 4, 2016, both of which applications are hereby incorporated byreference in their entirety.

FIELD

The present disclosure relates to automatic slack adjusters for vehiclebraking systems.

BACKGROUND

The following are hereby incorporated herein by reference, in entirety.

U.S. Pat. No. 4,776,438 discloses a brake adjustment indicator adaptedto be mounted to a mounting bracket which supports a brake air chamberon a surface of the mounting bracket opposite the brake air chamber withthe brake air chamber having a rod extending there through with one endof the rod adjacent the surface and connected by a clevis pin to a brakearm.

U.S. Pat. No. 5,699,880 discloses a brake adjustment indicator for abraking system including a pressure chamber, a pushrod extendinglongitudinally outwards from the pressure chamber and moveable whencorrectly adjusted between first and second positions, a brake arm and apivot for pivotally mounting the pushrod to the brake arm.

U.S. Pat. No. 5,762,165 discloses indicia applied to opposite sidesurfaces of a housing of a slack adjuster for vehicle brakes and apointer is fixed for movement with a connector serving to pivotallyconnect the housing to a brake operating rod; the pointer cooperatingwith the indicia to provide visual indication of when the brakeoperating rod is in a retracted brake release position and when movementof such operating rod away from the brake release position exceeds adesired limit of brake operating movement.

U.S. Pat. No. 6,314,861 discloses a diaphragm-based spring brakeactuator assembly which allows for the delivery of more force to thepush rod without increasing the size of the actuator unit.

U.S. Pat. No. 8,302,742 discloses an improved self-adjusting automaticslack adjuster for reducing slack in the brake of a vehicle, in which aone-way clutch assembly is arranged in the housing of the automaticslack adjuster housing such that a thin-wall region of the housingassociated with the gear drive of the one-way clutch assembly is locatedoutside of a load path through which brake applications forces areconveyed from a brake actuator to a brake cam shaft upon which theautomatic slack adjuster is located.

U.S. Pat. No. 8,302,744 discloses an improved automatic slack adjusterfor reducing slack in the brake of a vehicle, in which a one-way clutchassembly is arranged at a side of the automatic slack adjuster housing,and one-way motion-inhibiting pawls in the one-way clutch assembly acton one-way gear teeth disposed on an inner radius of a gear wheel withinthe assembly whose outer circumference drives a slack adjuster unit.

U.S. Pat. No. 8,672,101 discloses an improved self-adjusting automaticslack adjuster for reducing slack in the brake of a vehicle, in which aneasily accessible external operating feature permits the automatic slackadjuster's one-way clutch assembly to be readily disengaged to allowsmooth release and retraction of the brake shoes of a vehicle brakewithout damage to the one-way teeth of the clutch assembly.

U.S. Pat. No. 9,267,562 discloses a brake chamber stroke indicatorsystem for a brake system including a brake air chamber includes anindicator rod or a string pot gauge including a housing with anindicator rotatably positioned within the housing.

U.S. Pat. No. 9,447,832 discloses a vehicle brake monitoring systemcomprises at least one sensor for detecting relative rotational positionof a brake camshaft during vehicle braking.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure includes the following drawing figures:

FIG. 1 depicts a side view of an example slack adjuster according to thepresent disclosure connected to a braking system (a partial portion ofthe braking system is depicted in FIG. 1). A piston rod of the brakingsystem is in a retracted position and the automatic slack adjuster is ina rest position.

FIG. 2 is a view like FIG. 1 in which the piston rod is in an extendedposition and the automatic slack adjuster is in a braking position.

FIG. 3 is a perspective view of an example slack adjuster of the presentdisclosure.

FIG. 4 is an exploded view of the slack adjuster of FIG. 3.

FIG. 5 is an enlarged, partial view of the slack adjuster of FIG. 3 witha sensor assembly disconnected from a cover plate.

FIG. 6 is a side view of internal components of the slack adjuster ofFIG. 3. In particular, a control gear, a pinion gear, and a take-offgear are depicted. The sensor assembly is depicted in dashed lines.

FIG. 7 is a perspective view of another example slack adjuster of thepresent disclosure.

FIG. 8 is an exploded view of the slack adjuster of FIG. 7.

FIG. 9 is an enlarged, partial view of the slack adjuster of FIG. 7 withthe sensor assembly disconnected from the cover plate.

FIG. 10 is a side view of internal components of the slack adjuster ofFIG. 7. In particular, the control gear and the pinion gear aredepicted. The sensor assembly is depicted in dashed lines.

FIG. 11 is an example system diagram.

SUMMARY

This Summary is provided to introduce a selection of concepts that arefurther described below in the Detailed Description. This Summary is notintended to identify key or essential features of the claimed subjectmatter, nor is it intended to be used as an aid in limiting the scope ofthe claimed subject matter.

In certain examples, a vehicle braking system includes a piston rodextendable from an air brake chamber, a rotatable cam shaft, and a slackadjuster coupled to the piston rod and the cam shaft. The slack adjusteris configured to rotate the cam shaft as the piston rod extends. Theslack adjuster has a control gear coupled to the cam shaft such that thecontrol gear rotates as the cam shaft is rotated, a pinion gear thatmeshes with the control gear such that the pinion gear rotates as thecontrol gear rotates, a take-off gear that meshes with the pinion gearsuch that the take-off gear rotates as the control gear rotates, and amagnet coupled to the take-off gear and configured to rotate as thetake-off gear rotates. A sensor is configured to sense rotation of themagnet, and an indicator is configured to indicate brake stroke of thepiston rod.

In certain examples, a vehicle braking system includes an piston rodextendable from an air brake chamber, a rotatable cam shaft, and a slackadjuster coupled to the piston rod and the cam shaft. The slack adjusteris configured to rotate the cam shaft as the piston rod extends. Theslack adjuster has a control gear coupled to the cam shaft such that thecontrol gear rotates as the cam shaft is rotated, a pinion gear thatmeshes with the control gear such that the pinion gear rotates as thecontrol gear rotates, and a magnet coupled to the pinion gear andconfigured to rotate as the pinion gear rotates. A sensor is configuredto sense rotation of the magnet, and an indicator is configured toindicate brake stroke of the piston rod.

DETAILED DESCRIPTION

In the present disclosure, certain terms have been used for brevity,clarity and understanding. No unnecessary limitations are to be inferredtherefrom beyond the requirement of the prior art because such terms areused for descriptive purposes only and are intended to be broadlyconstrued. The apparatuses, methods, and systems disclosed herein may beused alone or in combination with other apparatuses, methods, andsystems. Various equivalents, alternatives, and modifications arepossible and are contemplated and included with respect to the examplesdisclosed herein.

FIGS. 1-2 depict a partial view of an example vehicle braking system 10having an slack adjuster 30 of the present disclosure. The brakingsystem 10 is configured to slow or stop a vehicle. The braking system 10includes an air brake chamber 12 which is mounted to the frame 14 of thevehicle. A pushrod or piston rod 16 is extendable from the air brakechamber 12 and is coupled to the slack adjuster 30 by a clevis 18. Theslack adjuster 30 is coupled to a cam shaft 20 that extends along a camshaft axis 21 and has a S-cam 22 (depicted in dashed lines) configuredto move brake shoes 24 into frictional engagement with a brake drum (notshown). When the brake of the braking system 10 is depressed by theoperator, the air brake chamber 12 is pressurized such that the pistonrod 16 is moved to an extended position (FIG. 2). Movement of the pistonrod 16 to the extended position causes the slack adjuster 30 to rotateto a braking position and rotate the cam shaft 20 which causes the S-cam22 to move the brake shoes 24 into frictional engagement with the brakedrum to thereby slow or stop the vehicle. When the brake of the brakingsystem 10 is released, the piston rod 16 retracts to a retractedposition (FIG. 1), the slack adjuster 30 returns to a rest position, andthe cam shaft 20 rotates such that the S-cam 22 does not engage thebraking shoes 24. The brake shoes 24 also retract a predetermineddistance or clearance from the brake drum. However, as the vehicle isoperated and the brake shoes 24 become worn, the slack adjuster 30, thecam shaft 20, and the S-cam 22 are required to rotate through a greaterangle to apply the brakes. As such the slack adjuster 30 automaticallychanges the angular position between the slack adjuster 30 and the camshaft 20 to reduce the shoe-to-drum clearance to a desired level (i.e. aprescribed running clearance). Reference is made to the aboveincorporated patents for more description of the operation of thebraking system and conventional slack adjusters.

Conventional manual slack adjusters must be routinely serviced andmanually reset in order to maintain proper clearance between the brakeshoes 24 and the brake drums. Conventional automatic slack adjusters aretypically designed with a preset running clearance and a ratchetingmechanism that automatically takes up excess movement caused by worncomponents. Conventional automatic slack adjusters are available fromWebb Brake Adjusters (Part No. WBA07135S) and Haldex (Part No.40020212). The Commercial Vehicle Safety Alliance (CVSA) regulatesin-service inspection criteria for commercial vehicles operating in theUS, Canada, and Mexico. Improper brake adjustment accounted for 18% ofout-of-service (OOS) citations issued from 2012 through 2014 (CVSA,Roadcheck 2014). Each OOS citation may result in immediate downtime forthe vehicle, repair expenses, and thus loss of revenue.

Conventional mechanical or electronic systems can be implemented on thevehicle to measure brake adjustment and/or brake stroke of the pistonrod. Mechanical systems are typically “eyes-on”, meaning that theoperator must get out of the cab and physically inspect each wheel endfor proper adjustment (e.g., see the mechanical systems disclosed inU.S. Pat. Nos. 4,776,438, 5,699,880, and 5,762,165, which are herebyincorporated by reference, in entirety). An advantage of these systemslies in reducing the amount of time required to perform the inspection;however, they typically require two people (one in addition to thedriver) to perform the inspection, offer only a partial reduction in theamount of inspection time required, and are often susceptible tointerference from external sources. Electronic systems vary inmethodology and precision (e.g., see the electronic systems disclosed inU.S. Pat. Nos. 7,373,224, 7,624,849, and 9,447,832, which are herebyincorporated herein by reference, in entirety). Certain electronicsystems provide only a “green light” indication of in-service orout-of-service status, while other electronic systems report the actualbrake stroke measurement. A drawback of these systems has traditionallybeen the high upfront cost.

Through research and experimentation, the present inventor hasrecognized that it is desirable to improve upon prior art systems thatsense and/or measure brake adjustment and/or brake stroke of the pistonrod. Thus, the present inventor has endeavored to develop improvedsystems and methods for efficiently and effectively monitoring andmeasuring brake adjustment and/or brake stroke of the piston rod and forproviding automatic feedback to the operator. Accordingly, theapparatuses, methods, and systems of the present disclosure requirefewer parts to measure brake stroke; reduce installation costs andassembly time when compared to conventional systems that measure brakestroke; minimize interference with other components of the brake systemwhen compared to conventional systems that measure brake stroke; andeliminate or reduce alignment procedures when installing the slackadjuster when compared to conventional systems that measure brakestroke.

FIGS. 3-6 depict an example automatic slack adjuster 30 having a body 32and a control arm assembly 33 that sets a reference point for automaticbrake adjustment. The control arm assembly 33 includes a cover plate 34that covers the internal components of the slack adjuster 30 (describedherein). The cover plate 34 includes a cutout 63 (FIG. 4) that isaxially above a magnet 38 (described herein). The cutout 63 can be anysuitable shape, and in certain examples, the shape of the cutout 63corresponds to the shape of the magnet 38. The cover plate 34 alsoincludes a groove 66 configured to receive a sealing gasket or O-ring 76(described herein). A control arm 35 fixedly couples the control armassembly 33 to the vehicle (e.g. the frame 14 of the vehicle).

The slack adjuster 30 includes several internal components, some ofwhich are detailed and described herein below. Reference is also made tothe above incorporated U.S. Patents for further detail and descriptionof internal components of manual and automatic slack adjusters. Acontrol gear 36 is coupled to the cam shaft 20, and a pinion assembly 40meshes or engages with the control gear 36 such that the pinion assembly40, or a component thereof, rotates as the control gear 36 rotates. Thepinion assembly 40 has a pinion axle 41, a pinion axis 43, and a piniongear 42 centered about the pinion axis 43. A take-off assembly 50 meshesor engages with the pinion assembly 40 such that the take-off assembly50, or a component thereof, rotates as the pinion assembly 40 and thecontrol gear 36 rotates. The take-off assembly 50 includes a take-offaxis 53 and a take-off gear 52 centered about the take-off axis 53. Thetake-off assembly 50 is positioned or recessed in a pocket 56 (FIG. 4)defined in the body 32. In certain examples, the pocket 56 is incommunication with a void or bore 57 in which the pinion assembly 40 isreceived. In certain examples, the take-off gear 52 is smaller than thepinion gear 42 (i.e. the radius R1 of the take-off gear 52 is less thanthe radius R2 of the pinion gear 42 (see FIG. 6)).

The present inventor has determined that in certain slack adjusters 30,the inclusion of the take-off assembly 50 is important to correctlysense the rotation of a magnet 38 (described herein) attached thereto.That is, the present inventor has recognized that pinion assemblies incertain slack adjusters may not be susceptible for coupling the magnet38 thereto (e.g. the pinion axle may rotate independently from thepinion gear; the pinion axle and/or pinion gear may not be conducive tocoupling the magnet 38 thereto). Accordingly, the present inventor hasdiscovered through research and experimentation that the inclusion ofthe take-off assembly 50 can provide a location to couple a magnet 38 tothe slack adjuster 30. In these example slack adjusters 30, a magnet 38is coupled the take-off assembly 50 such that the magnet 38 rotates asthe take-off assembly 50 rotates. That is, as the slack adjuster 30 andcam shaft 20 rotate (FIGS. 1-2), the control gear 36 rotates the piniongear 42 which in turn rotates the take-off gear 52 and the magnet 38(the motion arrows in FIG. 6 depict rotation of the control gear 36,pinion assembly 40, and the take-off assembly 50, note that oppositerotation is possible). The control gear 36, the pinion gear 42, thetake-off gear 52, and the magnet 38 rotate continuously regardless ofwhether or not automatic brake adjustment is being performed by theslack adjuster 30. The magnet 38 is positioned relative to or centeredon the take-off axis 53 such that the magnet 38 rotates about thetake-off axis 53. The take-off axis 53, the pinion axis 43, and the camshaft axis 21 are parallel to each other.

The magnet 38 is coupled to the take-off assembly 50, or componentthereof, by any suitable fastener (e.g. screw, adhesive). In certainexamples, the take-off gear 52 defines a cutout 54 (FIG. 4) in which thetake-off gear 52 and/or the magnet 38 is partially or completelyrecessed. The shape of the cutout 54 can vary (e.g. circular, discshaped, “D”-shaped) and in certain examples, the shape of the cutout 54corresponds to the shape of the magnet 38. The magnet 38 can also beintegral with the take-off gear 52. The magnet 38 can be a multi-polemagnet, and the size and shape of the magnet 38 can vary (e.g. themagnet 38 is a diametrically magnetized disc magnet).

Referring now to FIGS. 7-10 another example automatic slack adjuster 30is depicted. In this example, the magnet 38 is coupled to the pinionassembly 40 and there is no take-off assembly 50. The magnet 38 iscoupled to the pinion assembly 40 such that the magnet 38 rotates as thepinion assembly 40 rotates. That is, as the slack adjuster 30 and camshaft 20 rotate (FIGS. 1-2), the control gear 36 rotates the pinion gear42 which in turn rotates the magnet 38 (motion arrows M in FIG. 10depict rotation of the control gear 36 and pinion assembly 40, note thatopposite rotation is possible).

Both example slack adjusters 30 (the first example depicted in FIGS. 3-6and the second example depicted in FIGS. 7-10) includes a sensorassembly 70 having a sensor housing 72 that is coupled to cover plate 34and a sensor 74 configured to sense rotation of the magnet 38. That is,the sensor 74 is configured to continuously sense rotation of the magnet38 and send signals to a computer controller 100 (described furtherherein) corresponding to the sensed rotation of the magnet 38. Thesensor 74 is positioned axially along the pinion axis 43 or the take-offaxis 53 such that the cutout 63 (FIG. 4) provides a clear path betweenthe sensor 74 and the magnet 38. An O-ring 76 is sandwiched between thecover plate 34 and the sensor housing 72 and received in the groove 66to thereby form a fluid-tight seal between the sensor housing 72 and thecover plate 34. In alternate examples, the groove 66 can be omitted anda flat seal (not shown) can be sandwiched between the sensor 74 and thecover plate 34 to create the fluid-tight seal. Any suitable sensor 74that can sense rotation of a magnet can be used. Examples of suitablesensors are commercially available from Infineon (model Nos. TLE5009 andTLE5012B), AMS (model No. AS5132), and Avago (model No. AEAT-6600-T16).

Referring to FIG. 11, a controller 100 receives signals from thesensor(s) 74. The controller 100 can be located on the slack adjuster 30and/or can be located remotely from the slack adjuster 30. In someexamples, the controller 100 can be configured to communicate via wiredcommunication (such as the CAN bus), wireless communication (e.g.Bluetooth or BLE), or any other suitable communication system 104.Although FIG. 11 shows one controller 100, there can be more than onecontroller 100. Portions of the methods described herein can be carriedout by a single controller or by several separate controllers. Eachcontroller can have one or more control sections or control units. Thecontroller 100 can include a computing system that includes a processingsystem, storage system, software, and input/output (I/O) interfaces(e.g. operator interface device 150 having an indicator 151) forcommunicating with devices described herein and/or with other devices.The processing system can load and execute software from the storagesystem. The controller 100 may include one or many application modulesand one or more processors 102, which may be communicatively connected.The processing system may comprise a microprocessor and other circuitrythat retrieves and executes software from the storage system.Non-limiting examples of the processing system include general purposecentral processing units, applications specific processors, and logicdevices. The storage system can comprise any storage media readable bythe processing system and capable of storing software. The storagesystem can include volatile and non-volatile, removable andnon-removable media implemented in any method or technology for storageof information, such as computer readable instructions, data structures,program modules, or other data. The storage system can be implemented asa single storage device or across multiple storage devices orsub-systems.

The controller 100 communicates with one or more components of the slackadjuster 30 via one or more communication links 101, which can be wiredor wireless links. The controller 100 is capable of monitoring and/orcontrolling one or more operational characteristics of the sensor(s) 74and/or the operator interface device 150 and its various subsystems bysending and receiving control signals via the communication links 101.It should be noted that the extent of connections of the communicationlink 61 shown herein is for schematic purposes only.

The controller 100 is coupled to an operator interface device 150 havingan indicator 151. The operator interface device 150 can be located onthe slack adjuster 30 and/or can be located remotely from the slackadjuster 30 (e.g. in the cab of the vehicle). The type and configurationof the operator interface device 150 can vary from that which is shown.The operator interface device 150 can include one or more conventionalinterface devices for interfacing and/or inputting operator selectionsto the controller 100. Exemplary operator interface devices 150 includetouch screens, mechanical buttons, mechanical switches, voice commandreceivers, tactile command receivers, gesture sensing devices, and/orremove controllers such as personal digital assistant(s) (PDAs),handheld(s), laptop computer(s), and/or the like.

As described above, the controller 100 receives signals from the sensor74 that correspond to the relative rotation between the magnet 38 andthe body 32. The controller 100 is configured (programmed) to calculatethe brake stroke of the piston rod 16 based on the signal received fromthe sensor 74 (length P1 on FIG. 1 depicts the length of the piston rod16 when the piston rod 16 is in the retracted position and length P2 onFIG. 2 depicts the length of the piston rod 16 when the piston rod 16 isin the extended position; the brake stroke of the piston rod 16 is thedifference between length P1 and length P2). The brake stroke of thepiston rod 16 can be calculated in different ways. In one example, amemory 103 of the controller 100 has gear ratio values (e.g. gear ratiovalues for the control gear 36, the pinion gear 42, and/or the take-offgear 52) and a length of the control arm 35 stored thereon that areknown or measured attributes of the particular slack adjuster 30 towhich the sensor assembly 70 and/or sensor 74 is coupled (i.e. the gearratio values and the length of the control arm 35 can differ betweendifferent models and sizes of slack adjusters 30). The processor 102processes the signal from the sensor 74, the gear ratio values, and thelength of the control arm 35 to calculate the brake stroke of the pistonrod 16. The processor 62 can be configured to use formulas, softwareprograms, and/or software modules stored on the memory 103 to calculatethe brake stroke of the piston rod 16. In other examples, the gear ratiovalues and the length of the control arm 35 for a particular slackadjuster 30 being used can inputted into the controller 60 by theoperator.

In other examples, the controller 60 is configured to compare the signalreceived from the sensor 74 to values in a lookup table stored on thememory 103 to determine the brake stroke of the piston rod 16. Thelookup table includes preprogrammed values for the brake stroke of thepiston rod 16 that correspond to the sensed rotation of the magnet. Theprocessor 62 “looks-up” the signal received from the sensor 74 in thelookup table and selects the corresponding preprogrammed value for thebrake stroke of the piston rod 16 (e.g. a signal from the sensor is 85degrees of rotation which corresponds to 0.75 inches of brake stroke ofthe piston rod 16 based on the lookup table).

The controller 100 relays signals and/or information related to thecalculated brake stroke of the piston rod 16 to the operator interfacedevice 150. The operator interface device 150 visually depicts orindicates the brake stroke of the piston rod 16 (e.g. 0.95 inches ofbrake stroke, 1.65 inches of brake stroke). In alternative examples, theoperator interface device 150 indicates whether the brake stroke of thepiston rod 16 exceeds a maximum brake stroke value preselected andprogrammed into the system (e.g. a red light illuminates when the brakestroke value exceeds the maximum brake stroke value).

In certain examples, a vehicle braking system having a piston rodextendable from an air brake chamber and a rotatable cam shaft has aslack adjuster coupled to the piston rod and the cam shaft and beingconfigured to rotate the cam shaft as the piston rod extends. The slackadjuster has a control gear coupled to the cam shaft such that thecontrol gear rotates as the cam shaft is rotated; a pinion gear thatmeshes with the control gear such that the pinion gear rotates as thecontrol gear rotates; a take-off gear the meshes with the pinion gearsuch that the take-off gear rotates as the control gear rotates; and amagnet coupled to the take-off gear and configured to rotate as thetake-off gear rotates. A sensor is configured to sense rotation of themagnet, and an indicator is configured to indicate brake stroke of thepiston rod. The cam shaft has a cam shaft axis and the take-off gear hasa take-off axis that is parallel to the cam shaft axis and the magnet iscoupled axially along the take-off axis. The pinion gear is centeredabout a pinion axis that is parallel cam shaft and the pinion axis isradially positioned apart from or between the cam shaft axis and thetake-off axis. The slack adjuster defines a pocket in which the take-offgear is recessed, and the slack adjuster has a cover plate that isconfigured to cover the pinion gear, the take-off gear, and the magnet.The sensor is coupled to the cover plate such that the sensor is axiallypositioned relative to the magnet. The cover plate defines a cutout thatis axially positioned relative to the take-off axis to thereby provide aclear path between the sensor and the magnet. The sensor has an O-ring,and the cover plate defines a groove that is configured to receive theO-ring so as to form a fluid tight seal between the cover plate and thesensor.

In certain examples, a controller is in communication with the sensorand configured to control the indicator to indicate the brake stroke ofthe piston rod. The controller can be configured to determine the brakestroke of the piston rod based on the rotation of the magnet sensed bythe sensor. In certain examples, the controller has a memory that storesa length of the control arm and gear ratio values for the control gear,the pinion gear, and the take-off gear. The controller is configured tocalculate the brake stroke of the piston rod based on the length of thecontrol arm, the gear ratio values, and the rotation of the magnetsensed by the sensor. In certain examples, the memory stores a look-uptable that has values that correlate rotation of the magnet sensed bythe sensor to brake stroke of the piston rod. The controller isconfigured to compare the rotation of the magnet sensed by the sensor tothe look-up table to thereby determine the brake stroke of the pistonrod. In certain examples, the indicator is further configured to alertthe operator when the brake stroke of the piston rod is equal to orgreater than a maximum brake stroke value. The controller is alsoconfigured to control the indicator to alert the operator that the brakestroke of the piston rod is equal to or greater than the maximum brakestroke value stored on the memory based on the brake stroke of thepiston rod determined by the controller.

In certain examples, a vehicle braking system having a piston rodextendable from an air brake chamber and a rotatable cam shaft includesa slack adjuster coupled to the piston rod and the cam shaft and beingconfigured to rotate the cam shaft as the piston rod extends. The slackadjuster has a control gear coupled to the cam shaft such that thecontrol gear rotates as the cam shaft is rotated; a pinion gear thatmeshes with the control gear such that the pinion gear rotates as thecontrol gear rotates; and a magnet coupled to the pinion gear andconfigured to rotate as the pinion gear rotates. A sensor is configuredto sense rotation of the magnet, and an indicator is configured toindicate brake stroke of the piston rod. The cam shaft has a cam shaftaxis and the pinion gear has a pinion axis that is parallel to the camshaft axis. The magnet is coupled axially along the pinion axis.

What is claimed is:
 1. A vehicle braking system having a rotatable cam shaft, a brake chamber, and a piston rod that extends from the brake chamber, the vehicle braking system comprising: a slack adjuster coupled to the piston rod and to the cam shaft, the slack adjuster being configured to rotate the cam shaft as the piston rod extends from the brake chamber, the slack adjuster having a control gear coupled to the cam shaft such that the control gear rotates as the cam shaft rotates; an indicator configured to indicate a brake stroke of the piston rod based upon rotation of the control gear; and a sensor and a magnet configured to rotate as the control gear rotates, and wherein the sensor is configured to sense rotation of the control gear based upon rotation of the magnet; wherein the slack adjuster further comprises a pinion gear that is coupled to the control gear such that rotation of the control gear causes rotation of the pinion gear.
 2. The vehicle braking system according to claim 1, wherein the magnet is coupled to the pinion gear.
 3. The vehicle braking system according to claim 2, further comprising a cover plate that covers the pinion gear and magnet, and wherein the sensor is coupled to the cover plate.
 4. The vehicle braking system according to claim 3, wherein the slack adjuster has a control arm, wherein the controller has a memory that stores a length of the control arm and gear ratio values for the control gear and the pinion gear, and wherein the controller is configured to calculate the brake stroke of the piston rod based on the length of the control arm, the gear ratio values for the control gear and the pinion gear, and the rotation of the magnet sensed by the sensor.
 5. The vehicle braking system according to claim 1, wherein the slack adjuster further comprises a take-off gear that is coupled to the pinion gear such that rotation of the pinion gear causes rotation of the take-off gear.
 6. The vehicle braking system according to claim 5, wherein the magnet is coupled to the take-off gear such that rotation of the take-off gear causes rotation of the pinion gear.
 7. The vehicle braking system according to claim 6, further comprising a cover plate that covers the pinion gear, take-off gear, and magnet, and wherein the sensor is coupled to the cover plate.
 8. The vehicle braking system according to claim 7, wherein the slack adjuster has a control arm, wherein the controller has a memory that stores a length of the control arm and gear ratio values for the control gear, the pinion gear, and the take-off gear, and wherein the controller is configured to calculate the brake stroke of the piston rod based on the length of the control arm, the gear ratio values, and the rotation of the magnet sensed by the sensor.
 9. A vehicle braking system having a rotatable cam shaft, a brake chamber, and a piston rod that extends from the brake chamber, the vehicle braking system comprising: a slack adjuster coupled to the piston rod and to the cam shaft, the slack adjuster being configured to rotate the cam shaft as the piston rod extends from the brake chamber, the slack adjuster having a control gear coupled to the cam shaft such that the control gear rotates as the cam shaft rotates; an indicator configured to indicate a brake stroke of the piston rod based upon rotation of the control gear; a sensor and a magnet configured to rotate as the control gear rotates, and wherein the sensor is configured to sense rotation of the control gear based upon rotation of the magnet; and a controller in communication with the sensor and configured to control the indicator to indicate the brake stroke of the piston rod, wherein the controller is configured to determine the brake stroke of the piston rod based on the rotation of the magnet sensed by the sensor.
 10. The vehicle braking system according to claim 9, wherein the controller has a memory that stores a look-up table correlating rotation of the magnet to brake stroke of the piston rod; and wherein the controller is configured determine the brake stroke of the piston rod by comparing the rotation of the magnet sensed by the sensor to the look-up table.
 11. The vehicle braking system according to claim 10, wherein the controller is further configured to control the indicator indicate when the brake stroke of the piston rod is equal to or greater than a maximum brake stroke value stored in the memory. 